The present invention generally relates to a process for the vulcanization of elastomeric products for example, of synthetic rubber, elastomeric plastics, etc., and more particularly, to an improved method of preheating green tires for pneumatic tires, soild tires and the like up to a predetermined temperature prior to vulcanization thereof by a vulcanizing machine.
Conventionally, in the vulcanization of elastomeric products such as a green tire having a thick portion with a large heat capacity, there are such disadvantages that, if the green tire is heated at high temperatures to achieve the best state for vulcanization up to a central portion of its thick portion, the outer portion of the green tire is undesirably brought into a state of over-vulcanization when the central portion thereof has reached the optimum state for vulcanization, with an excessive waste of thermal energy involved. Therefore, it has been a general practice to effect a preheating operation by which the elastomer product is preheated up to a predetermined temperature prior to the vulcanization thereof.
For the preheating as described above, a preheating process through irradiation by microwaves (i.e. dielectric heating) has been mainly employed owing to such advantages that, first, by the dielectric heating, the temperature rise begins at the inner-portion of the elastomer product which is most difficult site for the temperature to be increased during conduction heating, i.e. at the central portion thereof where the vulcanization is generally delayed, for example, at the innermost portion of a tread of the green tire. This is very desirable from the viewpoint of proper vulcanization. Secondly, reduction of the total time required for the vulcanization becomes possible, since the predetermined preheating temperature may be reached in a comparatively short period of time.
However, in a conventional preheating method of an oven system in which the preheating is effected in a preheating chamber through application of microwaves directed at an elastomer product mounted on a turntable, from a waveguide provided thereover, when a green tire, which normally has different thicknesses and rubber components in a radial direction, is to be processed, deviation in the preheating temperatures inevitably takes place in the radial direction, thus resulting in a non-uniformity of preheating temperatures in the green tire on the whole.